Prior art U.S. Pat. No. 3,927,942 provided a centrally apertured planar base plate for holding a sheet of unexposed photographic film thereon by a vacuum source and a cable guided overlying transparent sheet supporting a film containing an image to be reproduced and moved in an orbital or linear direction in unison with the transparent sheet relative to the unexposed film by a control knob mandrel manually inserted into and guided along a template supported by the base.
The principal disadvantage of the device disclosed by this patent is the manual operation which requires the operator to achieve smooth orbital or linear motion of the film containing the image when attempting to trace a template with a mandrel. Repeated consistent and uniform exposures are difficult to achieve by this prior art.
Other techniques presently used for obtaining modification of artwork images include handwork methods and light diffusion methods. The handwork method requires a high level of skill on the part of the workman and considerable time to obtain satisfactory results. The time factor is directly proportional to the number of images, such as letters forming words to be modified by hand. The light diffusion method is useful only for plus and minus images and is limited to a very small quantity of modification. Light diffusion is accomplished by interposing a clear film spacer between the image bearing film and an unexposed film. The exposing light is moved angularly around the films allowing the light to strike in at all angles to undercut the perimeter of the image forming a modified image on the exposed film. This method achieves approximately one-half millimeter undercut of the image for each exposure and additional exposures to obtain further undercuts results in loss of definition and a resulting poor quality of image. Further, when using this method of modification it is difficult to obtain identical and predictable results.